In recent years, in particular, materials for forming a color image have been mainly used as an image recording material. Specifically, recording materials of ink jet system, recording materials of heat-sensitive transfer system, recording materials of electrophotographic system, silver halide photosensitive materials of transfer system, printing inks, recording pens, and the like, have been used extensively. Color filters are used in image pick-up elements, such as CCD for photographing equipment, and in displays, such as LCD and PDP, to record and reproduce color images.
In these color image recording materials and color filters, dyes (dyestuffs or pigments) of three primary colors based on a so-called additive color mixing method or subtractive color mixing method are used, to display or record full-color images. A dye, which has absorption characteristics that enable the acquisition of a preferred color reproduction range and has (color)fastness against various conditions for use and environmental conditions, is not available yet, and improvement is strongly desired.
Because of inexpensive material costs, capability of high-speed recording, reduced noise in recording operations, and ease in color recording, ink-jet recording has rapidly come into wide use and is being further developed.
Ink jet recording methods include a continuous method in which droplets are supplied continuously and an on-demand method in which droplets are supplied in response to an image information signal. Ink discharge systems include: 1) one in which droplets are discharged by applying pressure with a piezoelectric element, 2) one in which droplets are discharged by producing air bubbles in ink with heat, 3) one using ultrasonic waves, and 4) one in which droplets are discharged by electrostatic suction. Aqueous ink, oil-based ink, and solid (molten) ink are used as ink-jet-recording ink.
The properties required for a dye that is used in the ink-jet-printing ink are: good solubility or dispersibility in a solvent; capability of high-density recording; good hue; fastness to light, heat, an active gas in environment (e.g. oxidative gases such as ozone, NOx, as well as SOx); excellent fastness to water and chemicals; good fixation and little blur on image-receiving materials; excellent storability as ink; being free from toxicity; high purity; and being available inexpensively. However, it is very difficult to provide a dye that satisfies these requirements on a high level. Particularly, it is strongly desired that a dye should have a good yellow hue, and fastness to light, humidity and heat, and in particular, fastness to an oxidizing gas such as ozone existent in environment when it is printed on an image-receiving material having an ink-receiving layer containing porous white inorganic pigment particles.
Generally, toners containing a colorant dispersed in resin particles are widely used in color copiers and color laser printers of electrophotographic system. The properties required for the color toners include absorption characteristics that enable the acquisition of a preferred color reproduction range, high transmission (transparency) which becomes a problem in particular, when they are used in an over head projector (hereinafter abbreviated to OHP); and (color)fastness against various factors under environmental conditions when using. Toners containing a pigment as a colorant dispersed in particles are disclosed in JP-A-62-157051 (“JP-A” means unexamined published Japanese patent application), JP-A-62-255956 and JP-A-6-118715. Although these toners have excellent light resistance, they easily aggregate since they are insoluble in a solvent, thereby causing problems such as a reduction in transparency and a change in hue of transmitted color. On the other hand, toners containing a dye as a colorant are disclosed in JP-A-3-276161, JP-A-7-209912 and JP-A-8-123085. These toners have rather high transparency and have no change in hue but have a problem with light resistance.
Heat-sensitive transfer recording has advantages, for example, that an apparatus thereof is small in size and can be reduced in production cost, that its operation and maintenance are easy, and that its running cost is low. The properties required for dyes used in thermosensitive transfer recording include absorption characteristics that enable the acquisition of a preferred color reproduction range, compatibility between thermal migration and fixability after transfer, thermal stability, and various types of colorfastness of the obtained image. Conventionally known dyes satisfy not all of these properties. For example, JP-A-60-2398 proposes a heat-sensitive transfer recording material and an image-forming method, which chelate-form a thermally diffusible dye by means of transition metal ions previously added to an image-receiving material, for the purpose of improving fixability and light resistance. However, the formed chelate dye has absorption characteristics at an unsatisfactory level and involves an environmental problem because a transition metal is used.
Since a color filter needs to have high transparency, a method called a dyeing method, in which the color filter is colored with a dye, has been carried out. For instance, a photoresist which can be dyed is subjected to pattern exposure and development to form a pattern, and then the resulting pattern is dyed with a dye of filter color. Subsequently, these steps are repeated for all the colors of the filter, to produce a color filter. Besides the above dyeing method, a color filter can also be produced by a method using a positive-type resist as disclosed in U.S. Pat. No. 4,808,501 and JP-A-6-35182. These methods provide a color filter which has high transmittance due to use of a dye, thereby being excellent in optical characteristics, but which has limitation, for example, to light resistance and heat resistance. Therefore, a dye which has excellent resistance to various factors and high transparency has been desired. Meanwhile, a method of using an organic pigment having excellent light resistance and heat resistance in place of a dye is widely known, but a color filter employing a pigment hardly gives optical properties equivalent to those when employing a dye.
Dyes for use in the above various applications must have the following properties in common. That is, they must have, for example, absorption characteristics preferred from the viewpoint of color reproduction, colorfastness under environmental conditions when they are used, such as light resistance, heat resistance, humidity resistance, resistance to an oxidizing gas such as ozone, and satisfactory fastness against chemicals such as a sulfurous acid gas.
In particular, dyes, which have a good yellow hue and colorfastness against light, moist heat and active gas contained in environment, particularly an oxidizing gas such as ozone, are strongly desired.
The typical skeleton of a yellow dye used in ink jet recording inks is an azo dye skeleton.
Typical examples of the azo dye include an aminopyrazole azo dye and a pyrazolone azo chelate dye disclosed in JP-A-57-5770 and JP-A-58-147470, a pyrazolone azo dye disclosed in JP-A-57-642775, a pyridone azo dye disclosed in JP-A-6-184481, stilbene azo dyes disclosed in JP-A-5-255625 and JP-A-5-331396, and a bisazo dye disclosed in JP-A-57-65757. JP-A-2-24191 discloses a thiadiazole-azo-pyrazole dye for thermal transfer. Further, in J. Soc. Dyers & Colourists, 102, 176-181 (1986), a dye having a triazinyl pyrazole skeleton is described, but its application to ink jet recording inks, heat-sensitive transfer ink sheets, color toners, and color filters is not disclosed therein.
These dyes are discolored or faded by oxidizing gases such as nitrogen oxide gas and ozone, which are often discussed as an environmental issue these days, with the result of a reduction in printing density. There are a large number of dyes that are not always satisfactory in terms of light resistance.
If the application field of the dyes is expanding and the dyes are widely used in exhibits such as advertisements in the future, it will be often exposed to light, heat, humidity and an active gas contained in environment. Therefore, a dye, which exhibits an excellent hue, and high fastness to light, moist heat, and an active gas in environment (e.g. an oxidizing gas such as NOx and ozone as well as SOx, etc.), and an ink composition of the dye, will be more and more strongly desired.
However, it is extremely difficult to find an azo dye and a yellow ink, which satisfy these requirements on a high level.